Sulfonylureas are known to be highly effective as herbicides and plant growth regulators. See, for example, U.S. Pat. Nos. 4,127,405; 4,169,719; 5,391,539; 5,488,029; 5,508,441; 5,580,842; 5,591,694; 5,599,769; 5,612,286; 5,635,450; 5,658,854; 5,688,745; 5,696,053; 5,714,436; and 5,747,421. However, aqueous solutions of sulfonylureas frequently degenerate within days and, therefore, cannot be stored for long periods of time.
There have been previous attempts to stabilize sulfonylureas in aqueous suspension compositions. For example, Sandell, U.S. Pat. No. 4,599,412, discloses a process for the preparation of solution formulations of sulfonylureas containing an agriculturally suitable cation, such as ammonium or substituted ammonium. Sandell also generally discloses that ammonium and quaternary ammonium salts of sulfonylureas can be prepared by treating the corresponding N-protonated sulfonylurea with an ammonium salt solution. Sandell notes, however, that these compounds are still susceptible to the degradative effects of moisture and impurities present in at least trace quantities in all practical solvent systems.
Hyson, U.S. Pat. No. 4,936,900, discloses compositions consisting essentially of a sulfonylurea and a carboxylic or an inorganic acid. No quaternary ammonium salts are disclosed.
Ort et al., U.S. Pat. No. 5,688,745, discloses salts of a sulfonylurea formed from bases, such as alkali metal carbonates, alkali metal hydroxides, alkaline earth metal hydroxides, ammonia, and ethanolamine, or acids, such as hydrochloric acid, nitric acid, trichloroacetic acid, acetic acid, and palmitic acid.
Schnabel et al., U.S. Pat. No. 5,696,053, is directed to a salt of a sulfonylurea containing a metal or ammonium ion.
Fory et al., PCT Publication No. WO 97/41112, discloses a salt of a sulfonylurea containing an alkali metal or alkaline earth metal atom.